Current internal combustion engines typically use one or more pistons in single, opposed, in-line or V arrangements. They use a crankshaft where the piston is connected to a crankshaft through a connecting rod. The crankshaft has one or more bearings offset from the center of the shaft that drive the pistons back and forth as the shaft turns to ingest and exhaust gases contained by the piston in a cylindrical space in the engine block. They operate with a constant displacement and constant compression ratio. Thus they are essentially constant displacement engines. Some attempts (such as in some Cadillac and Honda automobiles) have been made to vary displacement by inactivating use of certain cylinders in a multi-piston engine. The engine displacement is changed in discontinuous steps limiting fuel efficiency over a continuously variable displacement engine. Also, the frictional losses are not reduced in this design at reduced power and engine control becomes more complex.
Aircraft engines have also been designed with multiple pistons arranged in a radial manner around a single offset bearing on the crank shaft. This arrangement is used when high torque is required and the engine speed (rotations per minute) is not very high.
High speed rotary compressors and turbines have also been used in engine designs, primarily in aircraft applications, where air is drawn through the engine, mixed with fuel and combustion is internal to the engine. These applications are generally not suitable for land vehicle or industrial uses because of cost and low fuel efficiency.
Many factors affect the useful power that is produced by an internal combustion engine. The five main variables for a piston engine are the engine displacement, speed (rotations per minute), compression ratio, inlet air pressure and fuel-to-air ratio. Thermodynamic principles indicate that for an internal combustion engine of fixed displacement, maximum fuel efficiency (ratio of useful power to fuel consumed) of traditional engines occurs near the conditions of maximum inlet air pressure, which is also near the maximum power setting for a given engine speed. In internal combustion engine applications, the common method of controlling power produced is to lower intake pressure until the desired power level is produced. Thus the engine is normally operating at reduced efficiency.
U.S. Pat. No. 5,553,582, issued to Speas, shows an engine based on the wobble plate concept wherein the engine design is capable of varying engine displacement, cylinder compression ratio, valve timing and valve travel. The Speas design may be considered very complex, and may not be practical for an operational engine. The complex mechanisms in the Speas patent required to achieve all the variables are not needed in a fuel efficient engine and may prevent the design from being implemented.